Respirator masks are used in a wide variety of hazardous environments. Such environments include paint booths, grain storage facilities, laboratories with hazardous biological materials and environments containing certain chemical fumes. Respirator masks are typically adapted to receive a variety of filter units and other attachments that are designed specifically for the hazardous environment in which the mask is to be used. As such, the same mask body can be used in a variety of different hazardous environments simply by changing the filter. This ease of changing filters makes the masks very cost effective by permitting the manufacture of a single mask for multiple environments.
Respirator masks define a clean air envelope with the face of the wearer. The clean air envelope includes the clean air source and is bounded by the mask, the mask's seal with the face of the wearer, and the exhalation valve of the mask.
There are two general designs of respirator face masks: the partial facepiece mask and the full facepiece mask. A partial facepiece mask typically encloses the wearer's mouth and nose and forms a seal with the portion of the wearer's face that is contiguous to the nose and mouth. The eyes are left unprotected when using the partial facepiece mask. The full facepiece mask is a much larger unit and encloses the wearer's eyes in addition to the wearer's nose and mouth. Such masks include a transparent viewing portion to permit the wearer to see while wearing the mask.
Respirator masks can additionally be distinguished by being either a positive pressure or negative pressure device. A positive pressure device typically includes an external pump or pressurized vessel, with or without a filter, that is the clean air source and that forces air into the mask. Such a mask creates a more positively sealed clean air envelope about the wearer since the internal pressure in the clean air envelope created by the mask and the wearer's face is at a higher pressure than the environment around the mask. In this case, environmental air is not allowed to seep into the clean air envelope because it is restrained by the higher pressure inside the clean air envelope.
A negative pressure respirator mask functions on the negative pressure generated by the wearer inhaling. The inhalation generates a negative pressure inside the clean air envelope and draws air into the respirator mask. Generally, ambient air is drawn through a filter or filters by the negative pressure. The filters clean the air and the air is then drawn into the clean air envelope of the mask for inhalation by the wearer.
In the past, there has been substantial work performed in attempting to provide a means for the wearer of a breathing apparatus to communicate orally. Inactive devices are purely mechanical devices and active devices involve some form of enhancement by powered amplification. The most common inactive communication device is the voice diaphragm. This is a sealing diaphragm that is designed to vibrate in response to the pressure waves in the mask that are generated by the wearer's speech. The prior art comprises two general categories of active speech transmission devices: internal devices and external devices. Internal devices are typically constructed integral to the mask itself. Such devices comprise microphones, light transmission, and magnetic transmission devices. The devices are mounted within the clean air envelope defined between the mask and the wearer's face. A desirable feature of the internally mounted devices is that they, in general, provide a louder volume and truer, more distinct reproduction of the speech of the wearer when compared to the externally mounted devices.
The internally mounted voice receivers generally require structural modification of the mask itself to mount the device within the mask. The devices typically require penetration of the mask to transmit the wearer's voice outside of the clean air envelope, involving further modification of the mask structure. This penetration is not necessarily a drawback where the voice transmission is required to be used in all cases when the mask is worn. Such instances include, for example, masks worn by the operators of high performance aircraft and masks worn by fire fighters. Structural modification and physical penetration of the mask are a distinct disadvantage in instances where the speech transmission is desired to be an optional feature to an existing mask design.
The active external devices are mounted outside the clean air envelope defined by the mask. Such devices typically have poorer quality sound transmission since the sound energy must penetrate a voice diaphragm or the like before being received by the speech transmission device. Such devices do not however penetrate the clean air envelope of the mask. These devices typically involve the use of transducers attached to the exterior of the mask to amplify the sound that is transmitted through a voice diaphragm. The diaphragm is a gas tight seal and may be a vibrating voice diaphragm or may be the exhalation diaphragm of the mask. Such external devices have the advantage that they can be designed to be readily added to existing masks by clip-on features and the like and thus may not require structural modification of the mask itself.
Examples of internally mounted active speech amplification units are typified by the devices of U.S. Pat. Nos. 4,989,596 and 4,980,926, and one embodiment of U.S. Pat. No. 4,508,936. Externally mounted speech transmission adapters are exemplified by the devices of U.S. Pat. Nos. 4,352,353, 5,138,666, 5,224,473, and 5,224,474.
It would be a decided advantage to have an enhanced speech transmission device that is readily adaptable to be attached to an existing mask that is produced in large quantities. The speech transmission adapter should produce excellent quality voice transmission. This requirement means that the adapter should be mounted inside the clean air envelope defined by the mask on the wearer's face. In order to minimize the cost impact of the adapter, it is highly desirable that the design not require any structural modifications to the basic respiratory mask as it is produced without an enhanced voice transmission device.